Nasrin Sotoudeh had been serving a six-year sentence after being arrested in September 2010 and convicted of spreading propaganda and conspiring to harm state security.
Her husband Reza Khandan told Reuters Sotoudeh was dropped off at their home by prison authorities on Wednesday evening.
“It’s not a temporary release, it’s freedom,” Khandan said by phone from Tehran. “They put her in a car and dropped her off at the house.”
Iranian President Hassan Rouhani, who took office last month, pledged during his election campaign to ease some political and social restrictions, and his supporters have called for the release of political prisoners.
However, authorities gave Sotoudeh no reason for the release and offered no details on who had ordered it, Khandan said.
“We are all so happy from the depths of our hearts,” said Khandan. He and Sotoudeh have two children.
“But we are waiting for the last prisoner to leave prison,” he said. “Our joy will be complete then … The moment we are happy we think of others, those women who have been in prison for years without a single hour of furlough. It makes it difficult to be fully happy.”